The present invention relates basically to the control instrumentation and can be used for measuring physical-mechanical parameters of the environment and for nondestructive control of objects under diagnostics.
A tunnel nanodetector of mechanical vibrations is known, which comprises a sensor made in a shape of a flexible cantilever and secured at one edge, a tip probe, from which the electron tunneling occurs, a perforated counter-electrode designed for electrostatic control of the sensor and a fixed electrode. The electrodes enabling the occurrence of tunneling the electrons between them are plated with a noble metal, for example, gold. The action principle of the tunnel nanodetector is based on measuring the tunnel current running through the gap between an electrode of the sensor and the fixed electrode. The current value depends on the size of the gap. (W. C. Young, Roark""s Formulas for Stress and Strain, New York: Mc Graw-Hill, 1989).
A disadvantage of the known tunnel nanodetector of mechanical vibrations is an insufficient vibration-and shock strength and a high level of inherent noise, this doesn""t allow to carry out a reliable measuring of physical-mechanical characteristics of objects to be sensed.
A tunnel nanodetector of mechanical vibrations is known, which comprises a sensor made in a shape of a tip probe plated with a layer of a noble metal, over which at the level of from parts of nanometer to parts of micron a corrugated membrane is located being plated with a layer of a noble metal from the tip side, said layer of the noble metal is connected to the input voltage source. Additionally said tunnel nanodetector comprises a unit intended to control the gap value between the tip and membrane containing a deflection electrode made of a layer of the noble metal deposited around the tip, a tunnel current amplifier placed between the layer of the noble metal deposited on the tip and the first input of the A/D converter (Kenny T. W. et al. Wide-Bandwidth Electromechanical Actuators for Tunneling Displacement Transducers. Journal of Micromechanical Systems, vol.3, No 3, 1994, p.99).
In accordance with the task to be solved and the common character of structural features the above described tunnel nanodetector of mechanical vibrations is mostly close to the invention and has been chosen as a prototype.
However, the known tunnel nanodetector of mechanical vibrations doesn""t assure the needed super high sensitivity and magnification stability in the wide range of acoustical vibration energies what hinders to listen as the inherent noises of objects under diagnostics as the noises induced by background effects, therewith the system is adapted neither to the level nor to the spectrum of the input acoustic signal.
It is known a method for preparation of tunnel nanodetectors of mechanical vibrations based on using the planar semiconductor technology, which foresees the preparation and forming of plating layers for the tip and membrane of sensor, the forming of an insulation layer and forming of a plating layer for the deflection electrode.
In accordance with the known method the tip and the membrane of the sensor are prepared at two separated silicon substrates, but the unit for control the gap value between the probe and membrane, the tunnel current amplifier and the A/D converter are prepared at an individual ceramic substrate (Kenny T. W. et al. Wide-Bandwidth Electromechanical Actuators for Tunneling Displacement Transducers. Journal of Micromechanical Systems, vol.3, No 3, 1994, p.99).
In accordance with the task to be solved and the common character of structural features the known method of fabricating the tunnel nanodetector of mechanical vibrations is mostly close to the invention and has been chosen as a prototype.
However the known method doesn""t provide the required high accuracy and reproducibility of constructive-functional parameters of tunnel nanodetectors and is of a low economic efficiency.
A technical result of the invention is the development of a tunnel effect nanodetector of mechanical vibrations meeting the need to rise the sensitivity and to decrease the level of inherent noises when measuring the physical-mechanical parameters of objects under diagnostics, to increase the dynamic range by an order of magnitude during ultrasound examination of patients and to reduce the radiation level up to the safe dose, to provide the adaptation of the diagnostics system to be created on its basis to the level and to the spectrum of the input acoustical signal or to the value of acceleration coming from the diagnosed object as well as to provide the capability of revealing the micro structural faults in objects under diagnostics (in the field of power engineering, mechanical engineering, building).
The method for preparation of said tunnel effect nanodetector in conformity with the invention allows to assure a high sensitivity and reproducibility of their constructive-functional parameters and to provide high economic characteristics.
The essence of the invention consists in that the tunnel effect nanodetector of mechanical vibrations relates to the micro systems because several functional units with minimum sizes of all involved components are combined in a single body. Into that tunnel effect nanodetector comprising a sensitive element (sensor), consisting of a probe made in the form of a pin plated with the layer of a noble metal over which a corrugated membrane is placed with a gap, the size of which can change from parts of a nanometer to parts of a micron, the membrane from the side of the pin is plated with the layer of a noble metal connected to the source of input voltage, a gap control unit placed between the pin and membrane and containing a deflection electrode made of the layer of the noble metal deposited around the pin, a tunnel current amplifier located between the layer of the noble metal deposited on the pin and the first input of the A/D converter there is inserted a capacitance measuring unit, the inputs of which are connected to the deflection electrode and to the layer of the noble metal deposited on the membrane and the output is connected to the second input of the A/D converter. A unit for limiting the tunnel current value with its input connected to the layer of the noble metal deposited on the pin and with its output connected to the deflection electrode is put into the unit for control the gap between the pin and membrane. The through holes are made across the whole surface of the membrane and in the layer of the noble metal covering it.
The sensor, the gap control unit, the tunnel current amplifier, the capacitance measuring unit and the A/D converter are made in the form of monolithic integrated circuit, therewith the pin of the sensor is prepared from the single crystal silicon within the substrate body and the sensor membrane and the components of the gap control unit, tunnel current amplifier, capacitance measuring unit and A/D converter are made from the polycrystalline silicon.
The essence of the invention consists also in that the method for preparation of the tunnel effect nanodetector of mechanical vibrations being based on using the planar semiconductor technology and incorporating such steps as preparation of sensor""s pin and membrane, forming the plating layers of the latter, forming the insulation layer and forming the plating layer for the deflection electrode should be realized as follows:
The sensor""s pin and the recesses for membrane corrugations are formed within a monolith of silicon substrate, for this to achieve the mask layer of the silicon nitride is deposited from the gaseous phase, the photolithography is carried out followed by dry etching with forming the patterns of the pin and of recesses for membrane corrugations, the sections of silicon nitride mask layer to be removed are exposed to the reactive ion etching; the isotropic plasma-chemical etching, anisotropic reactive ion etching and local thermal oxidation are successively performed, thereafter the silicon nitride mask and also the layer of the silicon oxide are chemically stripped.
The insulation layer and the plating layers for the pin and the deflection electrode are formed, for this aim the silicon substrate is thermally oxidized and the silicon nitride layer is deposited from the gaseous phase, the vacuum deposition of the noble metal is performed, the photolithography is carried out followed by dry etching with forming the plating patterns of the pin and deflection electrode, the layer of the noble metal is exposed to the reactive ion etching, thereafter the mask layer is removed from the photoresist by plasma-chemical way.
The gap-forming layer is prepared, for this aim the layer of fusible phosphorous borosilicate glass is deposited from gaseous phase and fire-polished, the photolithography is carried out with obtaining the pattern of the gap-forming layer, the layer of the fusible phosphorous borosilicate glass is exposed to reactive ion etching, after that the high-melting layer of the silicon oxide is deposited from the gaseous phase.
The membrane plating layer is formed, for this purpose the vacuum deposition of the noble metal and photolithography are carried out with forming the plating pattern, the noble metal layer is stripped by the reactive ion etching, thereafter the mask layer is plasma-chemically removed from the photoresist.
The membrane and the elements (xe2x80x9cgatesxe2x80x9d) of electronic means of the tunnel effect nanodetector are formed, this requires to deposit a layer of polycrystalline silicon from the gaseous phase and to carry out the photolithography for forming the pattern of the membrane and of holes on its surface as well as patterns of components of electronic means of the tunnel effect nanodetector, the layer of polycrystalline silicon and the layer of membrane plating are exposed to reactive ion etching and the mask layer of the photoresist is stripped by the plasma-chemical way, after that the selective chemical etching of the gap-forming layer from the phosphorous borosilicate glass and the layer from the silicon oxide is performed through the holes in the membrane followed by flushing the substrate in running deionized water.